Field of the Invention
The invention relates to an electrostatic powder-spraying device with triboelectric powder charging by means of a powder pipe surrounding a delivery channel for the spray powder and of at least one displacement body located in the flow channel in order to boost the flow velocity, whereby the powder pipe is grounded on the outside and provided at least on its inside with a triboelectric material, which is arranged in the elctrostatic contact series at a distance from the material of the powder particles to be sprayed.
A comparable device for powder spraying is known from the German published specification No. 29 38 806. Therein the charging of the powder is done in a pipe-shaped nozzle element, whose flow channel is narrowed by a guide body, in order to increase the velocity and to produce a vortex. In addition, the outside of the nozzle is grounded or connected to high tension. Thereby the particles with opposite charges can be separated at a contact with the walling of the nozzle which is coated with a triboelectric material or displacement body. Reportedly the charging of the particles is improved through this device.
However, a separate electric field has to be introduced between the nozzle and the work piece to guide the charged particles towards the material. Since the electrostatic field varies with the points, edges and other protrusions of the workpiece, neutral zones are created on the workpiece. The coating powder can by this apparatus only to an insufficient extent reach the edges and crevices in the workpiece. As a result, the coating is uneven, which is the basic cause of early surface damage such as rust spots or the like, to the coated workpiece.
The invention departs from the electrostatic device for powder spraying as described above and aims towards the object of building such a device in the simplest manner. Deposition of the coating powder should be uniformly even in the case of workpieces with complicated configurations and the efficiency of this deposition should be increased.